Ensuring the integrity of oil and gas transport pipelines is a significant focus of the energy industry. Loss of integrity can result in significant adverse financial and environmental impact. Operating experience has shown that internal corrosion is the one of the main threats to pipeline integrity for flowlines and gathering lines carrying untreated produced fluids. The fluids transported through the pipelines may be inherently corrosive and may rapidly reduce the pipe wall thickness, thereby increasing the risk of a loss of pipeline integrity. Consequently, pipeline inspection and pipeline corrosion measurement are of importance to the industry.
Currently, the industry uses two types of corrosion detection sensors: movable and fixed. Movable pipeline inspection tools include tools such as in-line-inspection (ILI) tools or smart pigs travel inside the pipeline with fluid to assess the condition of pipelines. These tools may be equipped with sensors that measure the remaining wall thickness on the pipeline. The data provided by such inspection, however, is a lagging indicator of corrosion; corrosion must first occur and the wall thickness must first be reduced before corrosion may be detected. Furthermore, the time period between two consecutive inspections runs may be relatively long (e.g., more than 5 years), and substantial damage may progress in the interim. Early detection of corrosion would enable earlier corrective actions, more timely corrosion mitigation and/or intervention, and elimination and/or reduction of high consequence integrity loss events.
Fixed sensors may also be used for corrosion detection and/or measurement. Installation of fixed sensors or coupons along the pipeline length may provide real-time monitoring of pipeline conditions. Currently, corrosion coupons and/or corrosion rate measuring probes such as Electrical Resistance (ER) and Linear polarization Resistance (LPR) are used to measure corrosion rate in real-time, or at frequent interval in the pipeline at fixed location. These in-pipeline coupons/probes are only capable of providing corrosion information at a local point. However, pipeline corrosion may vary with location along the length due to topography and change in flow conditions in the pipeline. If fixed sensors are installed at a relatively less corrosive location in the pipeline, the sensors may present an inaccurate picture of the state of the pipeline. Identification of correct installation location may be critical in extracting appropriate information from these fixed sensors, but such information may be difficult to obtain. Consequently, a large number of such sensors may need to be mounted along the length of the pipeline to get accurate information on the state of the full pipeline.
Prior art technologies include U.S. Patent Publication No. 2003/0121338 for a pipeline pigging device for non-destructive inspection of the fluid environment in a pipeline. This disclosure includes a spherical, flowing fluid monitoring tool wherein the sensing element is at/near the surface of the sphere for directly measures the fluid characteristics as it flows along the line. Another prior art technology includes U.S. Patent Publication No. 2012/0279599 for an infrastructure corrosion analysis. This disclosure includes a pig-like device that collects pipeline wall corrosion data from a pipeline, analyzes the data, evaluates corrosion risk, and creates an implementation plan for the remediation of the pipeline. Still another prior art technology includes U.S. Pat. No. 7,282,928 for a corrosion measurement field device with improved harmonic distortion analysis (HDA), linear polarization resistance measurement (LPR), electrochemical noise measurement (ECN) capability. This disclosure includes a corrosion measurement device that measures corrosion of a structure exposed to a fluid using a multi-electrode system and where a sinusoidal signal is transmitted into the fluid through one electrode and response evaluated using a second electrode.
Consequently, there exists a need for a sensor that is capable of providing early detection of pipeline corrosion without relying on an ex post facto corrosion analysis. There also exists a need for a sensor that is capable of providing corrosion information along a length of a pipeline without regard to topography and/or change in flow conditions in the pipeline. There further exists a need for a sensor that can provide accurate and timely information about the state of a pipeline.